The best weapon is rather pointless if you do not know the tactics to use it properly. There have been quite a few times I have killed the character with all the good items when I am only using the basic loadout.

There is really no "best" weapons in tf2 as a whole because there are 9 classes with different playstyles and different weapons designed for those playstyles. You can probably judge which is the best primary, secondary, or melee weapon for a class, but there isn't one weapon that will beat all others. "Favorite weapons" are a different thing, not sure if that's what you meant or not...

Having said that, the Brass Beast isn't really good for anything except last-point defense. You basically become a sentry gun while using it, I prefer a bit more mobility and a faster spinup.

for the engie, the widowmaker, its nice that you dont need to reload and when you kill a enemy you can pick his stuff up which fills up your amo so you can continue shooting while the others reload theire weapons.